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This paper reports on the status of a comprehensive ten-year research and development effort toward hybrid system-in-foil (HySiF). In HySiF, the merits of high-performance integrated circuits on ultra-thin chips and of large-area and discrete electronic component implementation are combined in a complementary fashion in and on a flexible carrier substrate. HySiF paves the way to entirely new applications of electronic products where form factor, form adaptivity and form flexibility are key enablers. In this review paper the various aspects of thin-chip fabrication and embedding, device and circuit design under impact of unknown or variable mechanical stress, and the on-and off-chip implementation of sensor, actuator, microwave, and energy supply components are addressed. INDEX TERMS Hybrid integrated circuits, thin film circuits, flexible electronics, micro assembly, multichip modules, chip scale packaging.

Various aspects of ultra-thin chip technology for flexible electronics are presented and discussed, including ultra thin-chip fabrication, mechanical and electrical characterization, as well as chip assembly and imbedding. A stress sensor based on a stack of two ultra-thin, flexible CMOS chips indicates the particular advantages of the ChipfilmTM process technology, which is subject of this paper, when compared to other kinds of thin-chip fabrication.

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